Field of the Invention
The present invention relates to a wireless access system, and more particularly, to a method of performing resource stream alignment and an apparatus for supporting the same in a wireless access system supporting multi cell and device-to-device communication.
Discussion of the Related Art
It is commonly believed that future cellular networks need to be headed for more efficient harvesting and organization of existing spectral resources. Efficient reuse of the existing spectrum is heavily emphasized for next generation mobile networks (NGMN), characterized by heterogeneous and highly dense cell deployments. What we should carefully consider, however, is that the dense deployment of cellular networks occurs generating even more severe interferers from proximate areas. Hence, most users/nodes for wireless communications tend to inevitably suffer strong interference-limited regime, in particular as frequency reuse factor approximately converges to 1 due to spectrum scarcity. On the other hand, heterogeneous cell deployments induce various types of interference among hierarchical cell structures.
Multi-cell/layer coordination and cooperation techniques promise to unravel the aforementioned problems. After IEEE 802.16m [1] defines the first prototype of cooperation protocols, there are four classified ways of multi-cell/layer cooperation mostly concerned: inter-cell interference coordination, joint beamforming requiring shared channel state information (CSI), non-coherent joint transmission requiring shared user data but no CSI, and joint signal transmission requiring both shared user data and CSI. It is currently investigated and partially standardized in 3GPP LTE [2] that cooperative multi-point (CoMP) and inter-cell interference coordination (ICIC) promise to achieve significant gains because of its possibility to eliminate interferences. Recently, network assisted interference cancellation and suppression (NAICS) [3] can realize the desire for practical implementation of 1) linear minimum mean squared error (MMSE) and interference rejection combiner (IRC), 2) successive interference cancellation (SIC), and 3) maximum likelihood detector, in particular to evaluate potential gains of advanced user equipment (UE) receivers with network assistance.
Under the tendency of networks being smaller and denser cell deployments, moreover, the number of UEs per serving cell is also decreased. Different from a symmetric uplink-downlink (UL-DL) assignment in conventional ways, the small number of UEs to be served makes traffic rate demands and channel conditions more dynamic; thus it may require a re-distribution of UL-DL resources within a cell. An asymmetric UL-DL assignment brings out different kinds of interference due to the traffic adaptation in adjacent cells, especially on time division duplex (TDD). The technique currently considered in this situation, namely enhancements to LTE TDD for DL-UL interference management and traffic adaptation (eIMTA) [4], provides mechanisms that allow dynamic switching between UL-DL TDD resources.
[1] IEEE Computer Society, “IEEE standard for local and metropolitan area networks—part 16: air interface for broadband wireless access systems,” IEEE, Tech. Rep., May 2011.
[2] 3GPP, “Work item: coordinated multi-point operation for LTE,” 3GPP, Tech. Rep., March 2012.
[3] 3GPP, “Study on network-assisted interference cancellation and suppression for LTE,” 3GPP, Tech. Rep., February 2013.
[4] 3GPP, “Evolved universal terrestrial radio access (E-UTRA); Further enhancement to LTE time division duplex (TDD) for downlink-uplink (DL-UL) interference management and traffic adaptation,” 3GPP, Tech. Rep., June 2012.
[5] S. Alamouti, “A simple transmit diversity technique for wireless communications,” IEEE J. Select. Areas Commun., vol. 16, pp. 1451-1458, October 1998.